[MINVOKER-377] Invoker plugin should sanitize environment it obeys

**[Tamas Cservenak](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=cstamas)** opened **[MINVOKER-377](https://issues.apache.org/jira/browse/MINVOKER-377?redirect=false)** and commented

Use case: let's use "split repository". All fine and dandy, you can set it in your `$HOME/.m2/settings.xml`. And your builds will use it. But, if you create IT using invoker, you have a problem:
* invoker:install observes "outer" build, and will _install the IT artifacts into split repository_
* invoker:run if use own settings, not using split, will fail to find anything in "it-repo"

Basically the env should be sanitized: install should produce local repo as run would use. As currently, there is not way to run ITs if split repo is used.

Similar to MINVOKER-372

---
No further details from [MINVOKER-377](https://issues.apache.org/jira/browse/MINVOKER-377?redirect=false)

Start by reading the related MINVOKER-372 issue and tracing how invoker:install and invoker:run handle settings and local repositories. Reproduce the split-repository case described here. Done means install targets the local repository that run will use, allowing integration tests to find the installed artifacts.

Written by the indexing model from the issue text.